As combinations of larger diameter wheels, lower profile tires and more rigid or sensitive corner suspension components are being employed in newer vehicle platforms, the vehicle wheel rotating bearing assembly is much more susceptible to receiving “Brinell marks” or “brinelling” due to low-speed side impacts with objects such as curbs, such as a 3-mph curb-impact, and radial impacts with objects such as potholes, with high-strength wheels and low-profile tires. Brinell marks are microscopic indents in the bearing raceway that occur as a result of impact force loads transmitted from a bearing mating attachment component through the bearing rolling elements. For example, a wheel mounting flange may sustain an impact force and transmit the force load to ball components which impact the bearing raceways of a ball bearing assembly. The typical result of a radial or side-impact Brinell event is the development of a noisy or vibrating bearing assembly in the vehicle.
A typical vehicle curb impact event produces a sudden high peak offset load to the centerline of the wheel bearing assembly. During this type of load the side forces quickly reduce the preload condition of the bearing rolling elements. The axial movement of the rotating component inward toward the nonrotating component then forces some of the balls to move outward radially as they are forced to move inboard along the arcuate profile of the inner ballraces. At the same time, because the load is offset (generated by a curb-height strike to the vehicle, which is typically offset from the wheel mounting axis by about 150-200 millimeters, there is also a resultant downward transverse force to the rotating component that causes the largest ballrace impact Brinell depths in the top region of the inboard ballrows and the bottom region of the outboard ballrows, thus generating the noise and/or vibration condition in these regions at the lowest impact state.
Similarly, a pothole radial impact event can produce quick forces to damage the bearing raceways, but this contact places the largest impact Brinell depths in the bottom region of the ballrows, as the impact forces are radial. Thus, in order to prevent low speed ballrace damage from both types of events (radial or axial), a combination of features or accompanying “contact” surfaces is required.
A common design solution is to increase the diametral or axial size of the bearing and/or the size or number of rolling elements of the bearing, which usually results in mass/weight and cost penalties and renders the bearing design inefficient in terms of straight running and cornering capabilities. Bearing raceway shoulder heights may also be increased with respect to the ball diameter to provide additional raceway support for the ball during an extreme side force event. This approach, however, raises processing costs. The penalty with all of the traditional ideas is the addition of mass/weight, rotational torque, and costs of the bearing and mating corner components to the bearing.
A need therefore exists for a bearing assembly having improved radial- and side-impact Brinell resistance without significant additional mass or reduced efficiency compared to existing bearing assemblies.